Rails’s Swappable Migration Backend for Schema Changes at Scale | Rails at Scale

This post explores Rails’s swappable migration backend, a little-known feature that lets applications customize how migrations run. At Shopify, we relied on monkey patches and a brittle SQL parser to make Rails migrations work with our Schema Migrations Service. We developed the swappable backend feature to more simply adapt Rails’s migration runner to our needs. We’ll cover why and how we built this, and how Shopify uses it to power database migrations at scale. .